The present invention relates to the recovery of gallium values from Bayer process liquors by liquid/liquid extraction and more particularly to an additive which enhances the kinetics of the gallium extraction.
U.S. Pat. No. 3,971,843 describes a process for recovering gallium from basic aqueous alkaline solutions thereof by means of a liquid/liquid extraction process utilizing certain substituted hydroxyquinoline chelating agents. The basic aqueous alkaline solutions also contain certain compounds of aluminum and sodium and are typified by sodium aluminate lyes originating from the Bayer process. Such gallium recovery method includes a liquid/liquid extraction stage, a separation stage, and a regeneration stage wherein the gallium is recovered by means of strong acids and the organic extraction phase regenerated for recycle.
A variety of acids have been proposed in the regeneration step of the process, depending upon the specific process configuration elected to be employed. These acids include, for example, hydrochloric, sulfuric, nitric, and hydrobromic acids.
In the gallium extraction stage, organic solvents for the substituted hydroxyquinoline reagents preferably are utilized. The art teaches organic solvents including long chain alcohols, e.g. n-decanol or isodecanol, various heavy phenols, and certain phosphoric esters, such as tributyl phosphate. The concentration of the substituted hydroxyquinoline reagents in the organic phase have efficacy at concentrations as low as 1% by volume and can range on up to 50% by volume of the organic phase. Typical concentrations, though, range from about 6% to 12% by volume in commercial operations.
Elevated extraction temperatures also have been shown to aid in the process, such temperatures ranging up to 100.degree. C. with 50.degree.-80.degree. C. being taught in the art to be preferred. So-called "decomposed" Bayer process liquids generally are treated in industrial practice. Such decomposed liquids are at a temperature in the vicinity of 50.degree. C.
The caustic sodium aluminate lyes from the Bayer process generally have a composition ranging from about 100-400 g/l Na.sub.2 O.sub.3 and 40-150 g/l Al.sub.2 O.sub.3, while typical "decomposed" liquors that industry prefers for solvent extraction of gallium range from about 150-200 g/l in Na.sub.2 O.sub.3 and about 70-100 g/l Al.sub.2 O.sub.3. Gallium levels in the "decomposed" liquor can range from as low as 80 to as much as 300 ppm gallium, though gallium levels can vary greatly depending upon the particular bauxite source used in the process.
A variety of kinetic rate enhancers or additives have been proposed in the art to be combined with the substituted hydroxyquinoline reagents. For example, U.S. Pat. No. 4,241,029 proposes the use of organic carboxylic acid compounds. U.S. Pat. No. 4,485,076 proposes the use of organo sulfates or sulfonates containing at least one acid functionality. U.S. Pat. No. 4,559,203 proposes the use of an organophosphorous compound with at least one acid functionality. U.S. Pat. No. 4,169,130, on the other hand, proposes to conduct the extraction step of the process under an inert gas atmosphere.